Conductive coatings are useful in a number of areas such as antistatic coatings, shielding applications, photo-imagable coatings and in photocopying applications. Although a number of conductive coatings are known in the prior art, there are limitations associated with their use.
One commercial type of conductive coating involves the use of high molecular weight, solvent-borne coatings which are not subsequently cured. Although these systems have good conductive characteristics, they are still subject to attack by solvent. For instance, if these coatings are used in a photo-imagable application, the electroconductive layer is typically topcoated with a dielectric layer. When both the dielectric and the conductive layer are coated from the same type of solvent, it is difficult to prevent the extraction of at least a small amount of the conductive material into the dielectric material thereby decreasing its effectiveness.
Radiation curable conductive materials are known in the art but these also have certain limitations. Prior to application, these coatings typically require the addition of free acrylic monomers for viscosity reduction. This is especially true when the polymer itself is an acrylic which has been prepared by free radical polymerization. The diluent acrylic monomers are often volatile and may contribute a toxicity hazard to the handling of the materials.
Many of the water-reducible coatings available in the prior art are relatively high in molecular weight and, therefore, must be reduced to less than about 50% solids for application. The excess water remaining in the coating must be driven off by heating, thereby using additional energy.
These problems are overcome in the present invention by using a water soluble, low molecular weight quaternary ammonium salt, which can be polymerized by subjecting it to actinic radiation. Since the product of this invention is a low molecular weight, water-soluble salt, low application viscosities can be achieved at high solids without the use of acrylic monomers and by using water as the only solvent. Once the salt of this invention has been cured by heat or actinic radiation, it is essentially impervious to attack by water or organic solvents.